1. Field of the Invention
This invention relates to a mirror follow-up device for a projector intended to project a continuously movable film upon an image plane, comprising a number of mirrors and a like number of ball-and-socket joints about each of which a mirror is pivotable as a function of the film speed for optical compensation of the movement of said film.
2. Description of the Prior Art
Projectors with optical compensation of the film movement are already known, comprising rotating polygonal prisms, where the parallel displacement of the light rays as a result of tilting of a plane parallel plate is utilized for the compensation of movement. With a prism of suitable dimensions, the virtual image produced inside is thereby kept constantly in repose, independently of the movement of the film. However, since additional image defects and discrepancies between the laws of motion of the film and of the beam of light occur, the projected image is not completely satisfactory. The use of such projectors remains essentially confined to auxiliary equipment for film production, e.g., editing tables.
Another projector with optical compensation which has also been proposed is the so-called Mechau projector, which comprises a circle of pivoting mirrors which cause the beam of light to follow the passing image and direct the moving beam coming from the image onto the screen. Via the optical system and a number of pivoting mirrors disposed therein and movable in all directions, which are situated on a rotating drum, the image from the front aperture is caused to follow the strip of film running downwards, with the aid of a prism, until a new pivoting mirror has meanwhile entered the path of rays and illuminates the next film image. The upwardly running image produced by the lens is then held steady by a pivoting mirror disposed opposite the abovementioned one and is directed onto the screen by a telephoto lens. The pivoting mirrors are disposed in a ring on the drum, which rotates around an axle, while the individual mirrors are guided in ball-and-socket joints in such a way that they guide the travel of the light beam in a corresponding manner and then cancel out this motion again. Although this projector is extraordinarily easy on the film, it has serious drawbacks. For one thing, it takes up a great deal of room, and the luminous flux obtainable is less than that of the known projectors having Maltese-cross transmissions.